The present invention relates to a device for positioning paper sheets which are sequentially driven out of a copier, facsimile machine, printer or similar image forming apparatus.
A sorter is available with a copier, for example, for collating or sorting paper sheets coming out of the copier into a plurality of bins. Positioning such paper sheets sequentially stacked on a bin, or receptacle, such that their four sides are accurately regulated is desirable from the handling standpoint. A neatly arranged paper stack can be stapled, punched, or otherwise treated, as desired. A device having a paper positioning member which is pivotable in abutment against one edge of paper sheets is known in the art.
However, none of prior art paper positioning devices of the type having a pivotable paper positioning device as mentioned above gives consideration to the moving speed of the paper positioning member, i.e., it has been customary to maintain the speed substantially constant. Specifically, when the pivoting speed is high, the paper positioning member abuts against one edge of a paper sheet with an excessive force. Hence, as the paper sheet is moved toward a paper positioning position and then restricted by a side wall or similar member of a receptacle, the resulting impact is apt to damage the edge of the paper sheet. At the same time, such an excessive force generates an excessive repulsive force in the paper sheet. Then, it is likely that the paper sheet once positioned is dislocated as the paper positioning member retracts away from the edge thereof.
Although the pivoting speed of the paper positioning member may be lowered to eliminate the above problem, a decrease in the pivoting speed directly translates into a decrease in paper handling efficiency. Specifically, a sorter or similar paper handling device for use with a copier, for example, is designed to operate at a higher linear velocity than the copier body. Therefore, a paper handling apparatus with such a low pivoting speed cannot follow the linear velocity of the copier body and, in turn, requires the linear velocity of the copier body to be lowered, resulting in low productivity of the entire copying system.
The prior art paper positioning member pivots only once while driving means associated therewith is operated once, i.e., it cannot pivot twice unless the driving means performs a predetermined angle of reciprocating rotary motion twice. The two pivoting movements is, therefore, not practicable without resorting to complicated control and without sacrificing the durability of the control and drive systems.
A paper positioning device is disclosed in Japanese Patent Laid-Open Publication (Kokai) No. 59-177251. This prior art device has a fence (paper edge receiving member) which protrudes upward from the sheet receiving surface of a receptacle, and a paper positioning member located to face the fence and movable toward and away from the fence. After paper sheets have been stacked on the receptacle between the fence and the paper positioning member, the positioning member is moved toward the fence to position the paper stack in cooperation with the fence. The paper positioning member is implemented as a simple positioning rod. A drawback with this scheme is that when the paper sheets are curled upward away from the receptacle, they slip upward when pushed by the paper positioning member at one side thereof. When the positioning rod itself or the receptacles have errors ascribable to the fabrication stage or the assembly stage or when the paper sheets are not uniform in length, paper sheets cannot be accurately positioned in some receptacles although they may be done so in the other receptacles. Another drawback with this prior art implementation is that such a paper positioning member or rod has to be located at opposite sides of paper sheets. This, coupled with the fact that the plurality of positioning means rotate individually for positioning paper sheets, makes it difficult to position paper sheets at a predetermined position with accuracy.
A paper positioning device capable of dealing with paper sheets of various sizes is disclosed in U.S. Pat. No. 3,910,568, for example. This prior art scheme positions paper sheets by varying the pivoting angle of a paper positioning member in matching relation to the paper size. Specifically, the pivoting angle is increased for comparatively small paper sizes and decreased for comparatively large paper sizes. However, the position at which the paper positioning member abuts against paper sheets changes from one paper size to another, so that the positioning accuracy is lowered depending on the paper size.
Another prior art paper positioning device is constructed such that a paper sheet is positioned on an inclined bin due to gravity, i.e., only in a direction perpendicular to an intended direction of paper entry. In this type of device, a paper positioning member is caused into a pivoting motion as soon as a paper sheet enters a bin with no consideration given to the timing for driving the positioning member relative to the movement of the paper sheet. Hence, the accuracy of positioning which relies on gravity as mentioned above is apt to decrease.
Regarding the amount of pivoting motion of the paper positioning member, all the prior art devices move it just to one widthwise edge of a paper sheet. This brings about a problem that when the width of paper sheets is short of a predetermined width due to errors or when they are curled, the positioning member fails to urge the paper sheets against the fence and, therefore, to position them accurately.
A paper positioning device is built not only in a sorter which is operable with an image forming apparatus but also in a finisher and an intermediate tray of a copier having a two-side copying function, etc. For such an application, the device has a table having a flat surface, and a rotatable plate positioned on the table. Every time a paper sheet is introduced into the device such that it extends over a horizontal portion of the rotatable plate and the table, the plate is moved toward the edge of the paper sheet to position the paper sheet. The paper sheet is laid not only on the table but also on the horizontal portion of the rotatable plate as mentioned above, so that a pushing portion of the plate may surely abut against the edge of the paper sheet. However, the paper sheet, especially the paper sheet laid on the table first, is apt to get into between the table and the horizontal portion of the rotatable plate. Then, the rotatable plate will miss the edge of the paper sheet when rotated for positioning purpose.